Uber is facing legal action in the UK from British drivers who claim the taxi-booking firm does not provide them with basic workers' rights.
The case is being brought by law firm Leigh Day on behalf of the GMB union.
It argues Uber does not currently ensure its drivers are paid the minimum wage or that they receive paid holiday.
It says Uber does not provide its drivers with the rights normally afforded to employees, claiming instead that they are "partners".
Uber operates a car hire smartphone app that connects passengers to drivers.
Using the app, passengers can request to be picked up from any location within London, or 300 other cities worldwide.
Passengers pay Uber for the journey, and it then passes on a percentage of that payment to the driver.
But Leigh Day's lawyers claim Uber's contract terms breach of UK employment law.
They also argue there are serious health and safety issues.
They alleged Uber does not ensure its drivers take rest breaks or work a maximum number of hours per week.
They argue this provides a substantial risk to all road users given that, according to Uber's chief executive, there will be 42,000 Uber drivers in London in 2016.
Leigh Day added there had been reports of drivers being suspended or deactivated by Uber after having made complaints about unlawful treatment, without being given any opportunity to challenge the claims.
The law requires that workers should not be denied the right to work for raising such issues.
A successful legal action against Uber could see substantial pay outs for drivers, including compensation for past failures by the company to make appropriate payments to what lawyers argue are their workers.
Nigel Mackay a lawyer in the employment team at Leigh Day said: "Uber not only pays the drivers but it also effectively controls how much passengers are charged and requires drivers to follow particular routes. As well as this, it uses a ratings system to assess drivers' performance.
"We believe that it's clear from the way Uber operates that it owes the same responsibilities towards its drivers as any other employer does to its workers. In particular, its drivers should not be denied the right to minimum wage and paid leave."
The case is the first to be brought against San Francisco based firm in the UK although it has face legal action elsewhere around the world.
Last week taxi drivers in Canada's biggest city, Toronto, became the latest group to own legal proceedings against Uber.
The drivers are seeking C$400m (£198m) in damages and an injunction to stop the taxi-booking app from operating in the province of Ontario.
The action alleges that services like Uber X and Uber XL have created an "enormous marketplace" for illegal transportation in the city.
Taxi drivers in London have staged a number of protests over the company's operations. Last month, they launched a campaign to highlight their struggle with it.
Meanwhile, France has seen riots in response to Uber-Pop a subsidiary of Uber which allows unlicensed and untrained drivers to offer journeys to potential customers in their own cars.